A fire on Sunday damaged the house of the key witness to an arson attack which killed three Palestinians from the Dawabsheh family last summer in the West Bank village of Duma.

The house that caught fire on Sunday belonged to Ibrahim Dawabsheh, a relative and neighbour of the slain Dawabsheh family, who is the main witness in last summer’s attack. He and his wife were hospitalised for smoke inhalation and shock.

Last July, firebombing carried out by Jewish settlers killed a couple and their 18-month-old son in Duma. The couple’s five-year-old son was the sole survivor.

Israeli authorities are investigating the cause of the fire on Sunday on the second-floor home belonging to a relative of the Dawabsheh family.

Israeli police said they do not suspect of nationalist motives behind Sunday’s fire. A joint Shin Bet and police statement said the finding at the scene “are not compatible with characteristics that point to arson committed by Jews”. However, the police refused to further comment on the case due to a sweeping gag order that bans reporting details of the investigation.

Palestinian Authority Civil Defense organisation’s officials said their preliminary investigation showed the fire started on the master bedroom and spread to other parts of the house, causing extensive damage. Officials said they found evidence of highly flammable materials that were tossed into the bedroom through one of the windows. Duma residents said the fire was started after Molotov cocktails were thrown.